If you’re trying to send group MMS messages on an iPhone, go to Settings > Messages and turn on MMS Messaging. If you don't see an option to turn on MMS Messaging or Group Messaging on your iPhone, then your carrier might not support this feature.

If you receive messages on one device but not the other

If you have an iPhone and another iOS device, like an iPad, your iMessage settings might be set to receive and start messages from your Apple ID instead of your phone number. To see if your phone number is set to send and receive messages, go to Settings > Messages, and tap Send & Receive.

If you don’t have an iPhone, you can only send and receive messages with your Apple ID to other Apple devices using iMessage. To use iMessage, go to Settings > Messages > Send & Receive and make sure that you’re signed in with your Apple ID.

If you have issues with a group message

If you’re in a group message and stop receiving messages, check if you left the conversation. Open Messages and tap the group message. If you see a message that says you left the conversation, then either you left the conversation or you were removed from the group message. You can rejoin a group message only if someone in the group adds you.

You can also start a new group message. Here’s how:

Open Messages and tap .

Enter the phone numbers or email addresses of your contacts.

Write a message, then tap to send.

If you have other issues with a group message, you might need to delete the conversation and start a new one. To delete a group message:

Open Messages and find the conversation that you want to delete.

Swipe left over the conversation.

Tap Delete.

When you delete a message, you can't recover it. If you want to save parts of a message, take a screenshot. To save an attachment in a message, touch and hold the attachment, tap More, then tap Save.